1. Field of the Invention
The present invention relates generally to cross-connect systems, and more specifically to a cross-connect network node for monitoring signal quality for detection and restoration of link failure.
2. Description of the Related Art
In high-speed communication networks, it is the usual practice to provide a signal quality monitor circuit on a per-link basis. In the SONET (synchronous optical network) system, monitoring is performed on supervisory signals embedded in a time-division multiplexed signal, using the byte-interleaved parity contained in section, line and path overheads. However, the provision of monitor circuits on a per-link basis would result in an increase in the amount of OAM (operations, administration and maintenance) information which must be contained in the transport overhead of a frame. Additionally, if optical communication links are used for interconnecting nodes, routing of optical signals is implemented by an optical cross-connect switch without conversion to electrical signals. However, if monitor circuits are provided on a per-link basis, it is obviously disadvantageous that optoelectrical converters must be provided on a per-link basis.